refactor: change leetcode questions fetch method (#71)

## Description

Previously, leetcode questions are fetched using LeetCode GraphQL
Endpoints, which have stopped being publicly publicised due to security
concerns. As such, there might be a concern of scrapping if we were to
directly query LeetCode GraphQL endpoint. In this PR, we will be using a
[leetcode query
dependency](https://www.npmjs.com/package/leetcode-query) provided to
fetch the leetcode questions instead.

Author: xGladiate

backend-services/leetcode-backend-service/package-lock.json

@@ -28,6 +28,7 @@
     "bottleneck": "^2.19.5",
     "dotenv": "^17.2.2",
     "fastify": "^5.6.0",
+    "leetcode-query": "^2.0.1",
     "mongodb": "^6.20.0",
     "mongoose": "^8.18.1",
     "p-limit": "^7.1.1",

backend-services/leetcode-backend-service/package.json

@@ -1,11 +1,3 @@
-export const QUERY_LIST = `
-query problemsetQuestionList($categorySlug:String,$limit:Int,$skip:Int,$filters:QuestionListFilterInput){
-  problemsetQuestionList: questionList(categorySlug:$categorySlug, limit:$limit, skip:$skip, filters:$filters){
-    total: totalNum
-    questions: data { title titleSlug difficulty isPaidOnly questionFrontendId }
-  }
-}`;
-
 export const QUERY_DETAIL = `
 query question($titleSlug:String!){
   question(titleSlug:$titleSlug){

backend-services/leetcode-backend-service/src/leetcode/client.ts

@@ -6,12 +6,12 @@
  * to continue fetching more questions until all are processed.
  */
 import { Question, SeedCursor } from "../db/model/question.js";
-import { gql } from "./client.js";
-import { QUERY_LIST, QUERY_DETAIL } from "./queries.js";
-import type { BasicInformation, QuestionList, Details } from "./types.js";
+import { QUERY_DETAIL } from "./queries.js";
+import type { BasicInformation, Details } from "./types.js";
 import pLimit from "p-limit";
 import { logger } from "../logger.js";
 import { checkQuestionServiceHealth } from "../health.js";
+import { LeetCode } from "leetcode-query";
 
 const PAGE_SIZE = 200;
 /**
@@ -32,6 +32,8 @@ const DIFFICULTY_TIME_LIMITS: Record<string, number> = {
   Hard: 120,
 };
 
+const leetcode = new LeetCode();
+
 /**
  * Run one batch (default pageSize=200). Returns a summary.
  * @returns An object containing the result of the seeding operation.
@@ -63,10 +65,16 @@ export async function seedLeetCodeBatch() {
   let total = 0;
 
   try {
-    const { questionList: fetchedQuestionList, total: fetchedTotal } =
-      await fetchNonPaidQuestionList(pageSize, nextSkip);
-    questionList = fetchedQuestionList;
-    total = fetchedTotal;
+    const res = await leetcode.problems({ limit: pageSize, offset: nextSkip });
+
+    questionList = res.questions
+      .filter((p) => !p.isPaidOnly)
+      .map((p) => ({
+        titleSlug: p.titleSlug,
+        title: p.title,
+        isPaidOnly: p.isPaidOnly,
+      }));
+    total = res.total ?? res.questions.length;
   } catch (err) {
     logger.error(
       `Failed to fetch question list from LeetCode: ${(err as Error).message}`,
@@ -95,7 +103,6 @@ export async function seedLeetCodeBatch() {
 
   const questionInfos: QuestionDetail[] =
     await fetchNonPaidQuestionInfo(questionList);
-
   const ops = questionInfos.map((q) => ({
     updateOne: {
       filter: { titleSlug: q.titleSlug },
@@ -180,40 +187,14 @@ export async function fetchNonPaidQuestionInfo(
   return results.filter((d): d is QuestionDetail => d !== null);
 }
 
-/**
- * Fetch non-paid question list.
- * We will only store non-paid questions in our database because
- * content of paid questions will not be accessible without a premium account.
- */
-export async function fetchNonPaidQuestionList(
-  limit: number,
-  skip: number,
-): Promise<{
-  questionList: BasicInformation[];
-  total: number;
-}> {
-  const res = await gql<
-    QuestionList,
-    {
-      categorySlug: string;
-      limit: number;
-      skip: number;
-      filters: Record<string, unknown>;
-    }
-  >(QUERY_LIST, { categorySlug: "", limit: limit, skip: skip, filters: {} });
+export async function getQuestionDetail(slug: string) {
+  const res = (await leetcode.graphql({
+    query: QUERY_DETAIL,
+    variables: { titleSlug: slug },
+  })) as { data: { question: QuestionDetail | null } | null };
 
-  if (!res.problemsetQuestionList) {
-    throw new Error("Failed to fetch question list from LeetCode");
+  if (!res || !res.data || !res.data.question) {
+    return null;
   }
-
-  const { total, questions } = res.problemsetQuestionList;
-  const questionList = questions.filter((q) => !q.isPaidOnly);
-  return { questionList, total };
-}
-
-export async function getQuestionDetail(slug: string) {
-  const res = await gql<Details, { titleSlug: string }>(QUERY_DETAIL, {
-    titleSlug: slug,
-  });
-  return res.question;
+  return res.data.question;
 }

backend-services/leetcode-backend-service/src/leetcode/queries.ts

@@ -6,20 +6,13 @@ export type BasicInformation = {
   title: string;
   titleSlug: string;
   isPaidOnly: boolean;
-  difficulty: "Easy" | "Medium" | "Hard";
-  categoryTitle?: string | null;
-};
-
-export type QuestionList = {
-  problemsetQuestionList: {
-    total: number;
-    questions: BasicInformation[];
-  };
 };
 
 export type Details = {
   question:
     | (BasicInformation & {
+        difficulty: "Easy" | "Medium" | "Hard";
+        categoryTitle?: string | null;
         content: string | null;
         exampleTestcases?: string | null;
         hints?: string[] | null;